String.Replace is not working as expected

Question

I have a program

    public void TestMethod2()
    {
        string[] keywords =
        {
            "SELECT", "FROM", "WHERE", "GROUP", "HAVING", "ORDER", "LEFT",  "RIGHT", "JOIN", "INNER", "OUTER", "ASC",
            "DESC", "AND", "OR","IN", "BETWEEN", "BY", "NOT", "ON", "AS", "CASE", "WHEN", "ELSE", "UPDATE", "SET"
        };

        var actualString = "SELECT * FROm A Join B On C in D case e join t left outer join inner join right join";

        foreach (var text in actualString.Split(' '))
        {
            var isExists = keywords.Any(x => x.Equals(text, StringComparison.OrdinalIgnoreCase));

            if (!isExists)
            {
                continue;
            }

            actualString = actualString.Replace(text, text.ToUpper());
        }


        var expectedString = "SELECT * FROM A JOIN B ON C IN D CASE e JOIN t LEFT OUTER JOIN INNER JOIN RIGHT JOIN";

    }

I am a newbie in C#. I am not clear why the Replace() method is not working as expected. It is showing the output SELECT * FROM A JOIN B ON C IN D CASE e joIN t LEFT OUTER joIN INner joIN RIGHT joIN

Can someone please enlighten me why Replace() is behaving like this? Thanks in advance.

Answer 1

If you debug it you will notice that your keyword "in" replaces second join so you get joIN. Later your text variable will try to replace "join" with "JOIN" but it won't find "join" because part of it was uppercased.